I have no problem with the Big Three returning. It's more a matter of whether they'll take a back seat to a new cast or be at the forefront of the Star Wars action. I mean, Shatner made a return as Captain Kirk in Star Trek: Generations from the 1990s, after having been Kirk in the Original Series back in the 60s (as someone above already pointed out).

Though he did also die to pass the torch on to [Star Trek:] The Next Generation

My hesitation is not with them returning - by all means have them appear - it's, again, what kind of expectation they have for these characters to do. Harrison wouldn't have it so bad. He sits in a pilot chair and acts in front of a green screen or he can run around holding a blaster. With Leia I would rather see her remain a politician and not a Jedi, or at least not a Jedi with a lightsaber duel. The Mace-Sidious fight kind of showed how silly such a fight can be when you have actors that are not nimble enough for any kind of extended choreography (and Ian McDiarmid was apparently dreading that scene). Yeah, you can superimpose Carrie's face on a stunt double, but I still think fights like Dooku vs. Anakin/Obi-Wan and Sidious vs. Mace were definitely missing something that the fights like Luke vs. Vader, Qui-Gon/Obi-Wan vs. Maul, and Anakin vs. Obi-Wan had (or even Obi-Wan vs. Vader from ANH).

Luke engaging in a lightsaber fight seems inevitable. But again I'm hoping for something better than what we got with Sidious vs. Mace. Either they can simplify the fight to something like Obi-Wan vs. Vader, or they could do a big Force-filled fight like Palpatine vs. Yoda (where all Ian really had to do was stand there wave his arms and make angry/happy expressions and the artists did all the work of selling the idea that these two characters were moving massive objects and engaged in an epic fight of "magic" (not so different from the fights of Harry Potter).

Let us know how she looks so we can evaluate if she would be good enough to be in the new movie.

Why do her looks matter?

Offcourse she is going to look older but, I don't want her looking like a fat booze-hound on screen when VII comes out. At least if she looks a little decent I will be happy. Judging by her current pics on google she's not to bad lookin for an old bird. She will fit right in as an older, wiser Leia.

Hmm I wonder why Carrie Fisher had to be reshedule her late late show appearance so suddenly.
What a coincidence she was set for an interview on Craig's show so soon after the Disney/Starwars announcement.
I can't imagine anything else she planned to talk about.